Method of treating metals using amino silanes and multi-silyl-functional silanes in admixture

ABSTRACT

The invention relates to a method of improving corrosion resistance of a metal. The method comprises applying a solution containing one or more amino silanes in admixture with one or more multi-silyl-functional silanes to a metal substrate in order to form a long term corrosion resistant coating. The method is particularly suitable for use on cold-rolled steel, zinc, iron, aluminium and aluminium alloy surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 09/245,601,filed Feb. 5, 1999, now U.S. Pat. No. 6,132,808.

BACKGROUND OF THE INVENTION

The present invention relates to a method of metal treatment. Moreparticularly the invention relates to a method of improving corrosionresistance of a metal. The method has particular utility when the metalis to be subsequently painted, or operations such as bonding rubber tometals or bonding metals to metals are to be carried out subsequent tothe silane treatment. The method comprises applying a solutioncontaining one or more amino silanes in admixture with one or moremulti-silyl-functional silanes to a metal substrate in order to form acorrosion resistant coating. The method is particularly suitable for useon cold-rolled steel, zinc, iron, aluminium and aluminium alloysurfaces.

DESCRIPTION OF RELATED ART

Most metals are susceptible to some form of corrosion, in particularatmospheric corrosion including the formation of various types of rust.Such corrosion may significantly affect the quality of such metalsubstrates, as well as that of the products produced therefrom. Althoughcorrosion may often be removed from the metal substrates, theseprocesses are often, time consuming costly and may further diminish theintegrity of the metal. Additionally, where polymer coatings such aspaints, adhesives or rubbers are applied to the metal substrates,corrosion of the base metal material may cause a loss of adhesionbetween the polymer coating and the base metal. Such a loss of adhesionbetween a coating layer and the base metal may likewise lead tocorrosion of the metal.

Metallic coated steel sheet such as galvanized steel for example is usedin many industries, including the automotive, construction and applianceindustries. In most cases, the galvanized steel is painted or otherwisecoated with a polymer layer to achieve a durable andaesthetically-pleasing product. Galvanized steel, particularlyhot-dipped galvanized steel, however, often develops “white rust” duringstorage and shipment. White rust (also called “storage stain”) istypically caused by moisture condensation on the surface of thegalvanized steel which reacts with the zinc coating. White rust isaesthetically unappealing and impairs the ability of the galvanizedsteel to undergo subsequent process steps such as being painted orotherwise coated with a polymer. Thus, prior to such coating, the zincsurface of the galvanized steel must be pretreated in order to removethe white rust which is present, and prevent it from reforming beneaththe polymer layer. Various methods are currently employed to not onlyprevent the formation of white rust during shipment and storage, butalso to prevent the formation of the white rust beneath a polymercoating (e.g., paint).

It is well established that prevention of the formation of white rust onhot-dipped galvanized steel during storage and shipping can be achievedby treating the surface of the steel with a thin chromate film. Whilesuch chromate coatings do provide resistance to the formation of whiterust, chromium is highly toxic and environmentally undesirable.

It is also known to employ a phosphate conversion coating in conjunctionwith a chromate rinse in order to improve paint adherence and providecorrosion protection. It is believed that the chromate rinse covers thepores in the phosphate coating, thereby improving the corrosionresistance and adhesion performance. Once again, however, it is highlydesirable to eliminate the use of chromate altogether. Unfortunately,however, the phosphate conversion coating is generally not effectivewithout the chromate rinse.

Aluminium alloys are particularly susceptible to corrosion as thealloying elements used to improve the metal's mechanical properties(e.g., copper, magnesium and zinc) will decrease corrosion resistance.

Recently, various techniques for eliminating the use of chromate havebeen proposed. These include the steps of providing an aqueous alkalinesolution comprising an inorganic silicate and a metal salt in an amountto coat a steel sheet, followed by treating the silicate coating with anorganofunctional silane (U.S. Pat. No. 5,108,793).

U.S. Pat. No. 5,292,549 teaches the rinsing of metal sheet with anaqueous solution containing low concentrations of an organofunctionalsilane and a cross linking agent in order to provide temporary corrosionprotection. The cross-linking agent cross-links the organofunctionalsilane to form a denser siloxane film. The ratio range of silane tocross-linker is 20:1-2:1.

WO 98/30735 discloses a method of preventing corrosion using 2 treatmentsolutions, applied separately. The first solution employs amulti-silyl-functional silane cross-linker while the second solutionemploys an organofunctional silane.

U.S. Pat. No. 5,433,976 teaches the rinsing of a metal sheet with analkaline solution containing a dissolved silicate or aluminate, anorganofunctional silane and a cross-linking agent in order to form aninsoluble composite layer containing siloxane.

WO 98/19798 relates to a method of preventing corrosion of metal sheeteffected by the application of a solution containing one or morehydrolyzed vinyl silanes to the metal sheet. The method is particularlyuseful as a pretreatment step prior to painting of galvanized steel asthe vinyl functionalities promote the adhesion between the metal surfaceand the paint coating. A disadvantage, however, is that the vinylsilanes do not bond particularly well to the metal surface.

U.S. Pat. No. Re. 34, 675 (re-issue of U.S. Pat. No. 4,689,085)describes coupling agent and primer compositions which comprise aconventional silane coupling agent and bis (trialkoxy) organo compound,and partially hydrolyzed products of such mixtures.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofproviding long-term corrosion resistance to a metal substrate.

It is another object of the present invention to provide a method ofproviding a coating for long-term corrosion resistance to a metalsubstrate sheet which essentially employs a single-step treatmentprocess.

It is a further object of the present invention to provide a treatmentsolution for providing a coating for corrosion resistance to metalsubstrate, wherein the treatment composition need not be removed priorto painting.

It is a further object of the present invention to provide a treatmentcoating and solution for promoting rubber to metal bonding.

It is a further object of the present invention to provide a treatmentsolution for promoting metal to metal bonding using adhesives.

The foregoing objects may be accomplished, in accordance with one aspectof the present invention, by providing a method of improving corrosionresistance of a metal substrate, comprising of the steps of:

(a) providing a metal substrate, the said metal substrate chosen fromthe group consisting of:

steel;

steel coated with a metal chosen from the group consisting of: zinc,zinc alloy, aluminium and aluminium alloy;

iron;

zinc and zinc alloys;

aluminium; and

aluminium alloy; and

(b) applying a long-term coating on the metal substrate by contactingthe metal substrate with a solution containing one or more hydrolyzed orpartially hydrolyzed amino silanes, one or more hydrolyzed or partiallyhydrolyzed multi-silyl-functional silanes and a solvent andsubstantially removing the solvent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The applicants have found that corrosion resistance of metal,particularly cold-rolled steel, steel coated with a metal chosen fromthe group consisting of zinc, zinc alloy, aluminium and aluminium andaluminium alloy, aluminium and aluminium alloy per se and iron, can beimproved by applying a treatment solution containing one or morehydrolyzed or partially hydrolyzed amino silanes to said metal, whereinthe treatment solution additionally contains one or moremulti-silyl-functional silanes, having either 2 or 3 trisubstitutedsilyl groups, wherein the multi-silyl-functional silane(s) has been atleast partially hydrolyzed. The treatment solution forms a long-termcorrosion resistant coating upon curing.

The provision of a coating for long-term corrosion resistance issurprisingly superior to conventional chromate based treatments, andavoids the chromium disposal problem. In addition, the coating providessuperior adhesion of the metal substrate to paint, rubber, adhesive orother polymer layers.

In addition to the above mentioned corrosion preventative properties ofthe treatment method of the present application, the applicant has alsofound that the above mentioned coatings exhibit particular utility inthe promotion of rubber to metal bonding and metal to metal bondingusing adhesives.

The treatment methods of the present invention may be used on any of avariety of metal substrates including particularly cold-rolled steel,steel coated with a metal chosen from the group consisting of zinc, zincalloy, aluminium and aluminium and aluminium alloy, aluminium andaluminium alloy per se, and iron. The method of the present invention iseffected by applying a treatment solution containing one or morehydrolyzed or partially hydrolyzed amino silanes to said metal, whereinthe treatment solution additionally contains one or moremulti-silyl-functional silanes having either 2 or 3 trisubstituted silylgroups to the metal, wherein the multi-silyl-functional silane(s) hasbeen at least partially hydrolyzed.

As used herein, the term “substituted” aliphatic or aromatic means analiphatic or aromatic group wherein the carbon backbone may have aheteroatom located within the backbone or a heteroatom or heteroatomcontaining group attached to the carbor backbone.

The preferred amino silanes which may be employed in the presentinvention each have a single trisubstituted silyl group, wherein thesubstituents are individually chosen from the group consisting ofalkoxy, acyloxy and aryloxy. Thus, the amino silanes which maybe used inthe present invention may have the general structure

R is chosen from the group consisting of hydrogen, C₁-C₂₄ alkyl,preferably C₁-C₆ alkyl, C₂-C₂₄ acyl, preferably C₂-C₄ acyl, and each Rmay be the same or different. Preferably R is individually chosen fromthe group consisting of hydrogen, ethyl, methyl, propyl, iso-propyl,butyl, iso-butyl, sec-butyl ter-butyl and acetyl.

X is a group selected from the group consisting of a bond, a substitutedor unsubstituted aliphatic or aromatic group. Preferably X is selectedfrom the group chosen from the group consisting of a bond, C₁-C₆alkylene, C₁-C₆ alkenylene, C₁-C₆ alkylene substituted with at least oneamino group, C₁-C₆ alkenylene substituted with at least one amino group,arylene and alkylarylene

R¹ is a group individually selected from the group consisting ofhydrogen, C₁-C₆ alkyl, C₁-C₆ alkenyl, C₁-C₆ alkyl substituted with atleast one amino group, C₁-C₆ alkenyl substituted with at least one aminogroup, arylene and alkylarylene. Preferably R¹ is individually selectedfrom the group consisting of hydrogen, ethyl, methyl, propyl,iso-propyl, butyl, iso-butyl, sec-butyl ter-butyl and acetyl.

The particular preferred amino silane employed in the method of thepresent invention is γ-aminopropyltriethoxysilane, which will bereferred to as γ-APS, and having the structure:

More than one multi-silyl-functional silane may be employed in thetreatment solution. Each multi-silyl-functional silane has at least 2trisubstituted silyl groups, wherein the substituents are individuallychosen from the group consisting of alkoxy and acyloxy. Preferably themulti-silyl-functional silane of the present invention has the generalstructure.

wherein Z is selected from the group consisting of either a bond, analiphatic or aromatic group; each R³ is an alkyl or acyl group, and n is2 or 3.

Each R³ is chosen from the group consisting of hydrogen, C₁-C₂₄ alkyl,preferably C₁-C₆ alkyl, C₂-C₂₄ acyl, preferably C₂-C₄ acyl, and may bethe same or different. Preferably each R³ is individually selected fromthe group consisting of ethyl, methyl, propyl, iso-propyl, butyl,iso-butyl, sec-butyl, ter-butyl and acetyl.

Preferably Z is selected from the group consisting of a bond, C₁-C₆alkylene, C₁-C₆ alkenylene, C₁-C₆ alkylene substituted with at least oneamino group, C₁-C₆ alkenylene substituted with at least one amino group,arylene and alkylarylene. In the case where Z is a bond, themulti-functional silane comprises two trisubstituted silyl groups whichare bonded directly to one another.

The preferred multi-silyl-functional silane is1,2-bis-(triethoxysilyl)ethane , referred to as BTSE and having thestructure:

Other suitable multi-functional silanes include1,2-bis-(trimethoxysilyl)ethane (TMSE), and1,6-bis-(trialkoxysilyl)hexanes (including1,6-bis-(trimethoxysilyl)hexanes), 1,2-bis-(triethoxysilyl)ethylene,1,4-bis-(trimethoxysilylethyl)benzene, andbis-(trimethoxysilylpropyl)amine.

The above-described amino and multi-functional silanes must be at leastpartially, and preferably fully hydrolyzed so that the silanes will bondto the metal surface. During hydrolysis, the alkyl or acyl groups (i.e.,the “R” and “R³”, moieties) are replaced with a hydrogen atom. As usedherein, the term “partially hydrolyzed” simply means that only a portionof the alkyl or acyl groups on the silane have been replaced with ahydrogen atom. The silanes should preferably be hydrolyzed to the extentthat at least two of the alkyl or acyl groups on each molecule have beenreplaced with a hydrogen atom. Hydrolysis of the silanes may beaccomplished merely be mixing the silanes with water, and optionallyincluding a solvent such as an alcohol in order to improve solubility.

One significant advantage of the present invention is that the treatmentsolution may be applied directly onto the surface of the metal withoutthe need for an underlying layer of silicates, aluminate or othercoating. Another significant advantage is the utility and convenience tothe user of a one step treatment.

The present invention is particularly suitable if, subsequent totreatment of the metal substrate being carried out, the metal substrateis to be painted or coated with a polymer such as an adhesive or rubber.This may take place after one or more silane treatments, andadvantageously after curing of said silane treatment(s).

The pH of the solution is also preferably maintained below about 7, and,most preferably between about 3 and about 6, in order to improvehydrolysis. The pH may be adjusted, for example, by the addition of anacid, such as acetic, oxalic, formic or propionic acid. If the pH ispermitted to increase above about 7, the hydrolyzed multi-functionalsilane may begin to polymerize via a condensation reaction. If this ispermitted to occur, the corrosion resistance will be significantlyreduced since the silane may not bond strongly to the metal surface.

The concentration of multi-silyl-functional silanes such as BTSE in thesolution should be between about 0.01% and about 10%, preferably greaterthan 0.1%. More preferably, a concentration of between about 0.4% andabout 3%, most preferably about 2% is preferred.

The concentration of amino silanes in the solution should be betweenabout 0.01 and 10%. More preferably, a concentration of between about0.2% and about 2%, most preferably about 1% is preferred.

The ratio between the amino silanes and the multi-silyl-functionalsilanes is essential to the efficacy of the present invention inproviding long-term corrosion resitance. The term “long-term” as usedherein is relative to “temporary corrosion protection” coating, such asthat disclosed in the patent U.S. Pat. No. 5,292,549, in which itclaimed “the siloxane film may be removed by rinsing the metallic coatedsteel sheet in an alkaline solution prior to coating the sheet with aphosphate conversion coating and a paint.” In the context of corrosionresistance “long-term” means a coating which resists being washed off orremoved. The present invention shows superior properties on metalsurface and resists being removed by alkaline solution. This aspect canbe assessed by using an alkaline rinse solution, as set out in Example9, to try to remove the coatings of the present invention. The ratios ofamino silanes and the multi-silyl-functional silanes used in the presentinvention are in the range 4:1-1:8, preferably 2:1-1:4, more preferablya ratio of greater than 1:2.

Although a more concentrated solution will provide a greater filmthickness on the metal, this comes at the expense of increased cost. Inaddition, thicker films are often weak and brittle. The film thicknessis generally in the range of 0.05-0.2 μm.

It should be noted that the concentration of silanes discussed andclaimed herein are all measured in terms of the ratio between the amountof unhydrolyzed, multi-silyl-functional silanes employed (i.e., prior tohydrolyzation), and the total volume of treatment solution components(i.e., silanes, water, optional solvents and pH adjusting acids). Inaddition, the concentrations refer to the total amount of unhydrolyzedmulti-silyl-functional silanes added, as multiple silanes may optionallybe employed in this treatment solution.

The solution temperature is not critical. Temperatures down to 0C shouldbe satisfactory. There is no need to heat the solution but a temperatureof between 15 and 60° C. for the treatment bath during treatment will besatisfactory. Higher temperatures may cause polymerisation of the silane(i.e. they may shorten the bath life) and will have no benefit.

Since the solubility in water of some of the silanes used may belimited, the treatment solution may optionally include one or moresolvents, such as alcohols, in order to improve silane solubility. Thealcohol may also improve the stability of the treatment solution, aswell as the wettability of the metal substrate. The use of alcohols orother non-aqueous solvents such as acetone is also particularly usefufermetal substrates which re prone to corrosion upon contact with water(such as galvanic corrosion of certain alloys, including CRS).Particularly preferred alcohols include: methanol, ethanol, propanol,butanol and isomers thereof. The amount employed will depend upon thesolubility of the particular multi-silyl-functional silanes in thetreatment solution and thus the concentration range of alcohol to waterin the treatment solution of the present invention is in the ratio of1:99 to 99:1, (by volume). There should be sufficient water to ensure atleast partial hydrolysis of the silane, and thus it is preferable thatat least 5 parts of water be employed for every 95 parts of alcohol.Alcohols may, however, be omitted entirely if the silane(s) is solublein water. When alcohols are employed, methanol and ethanol are thepreferred alcohols.

Preparation of the treatment solution itself is straightforward. Theunhydrolyzed amino silanes are prehydrolyzed by diluting with water toobtain a desired concentration. The pH may be adjusted using an acid asdescribed above. The BTSE is prehydrolyzed by using a similar method andthe solutions are mixed and the pH be adjusted using acid. Alcohol mayoptionally be employed to aid solubility or stability as required. Inpractice the baths will be replenished with the silanes utilised in theinvention. These may be supplied pre-hydrolyzed and pre-mixed as a waterdilutable concentrate.

The metal substrate to be treated is preferably solvent and/or alkalinecleaned (by techniques well-known in the prior art) prior to applicationof the above-described treatment composition of the present invention.The treatment solution may then be applied to the cleaned metal byeither dipping the metal into the solution (also referred to as“rinsing”), spraying the solution onto the surface of the metal, or evenwiping or brushing the treatment solution onto the metal substrateIndeed any method which leaves a substantially even film on theserfacemay effectively be employed. When the preferred application method ofdipping is employed, the duration of dipping is not critical, as it willgenerally not affect the resulting film thickness. It is preferred thatthe dipping time be between about 2 seconds and about 50 minutes,preferably between about 0.5 minutes and 2 minutes to ensure completecoating of the metal.

If the metal is not to be coated with a polymer such as paint, andparticularly in the case of aluminium and aluminium alloys, the silanecoating should advantageously be cured following the application processdescribed above. Curing will polymerize the hydrolyzed silanol groups.The metal may be blown dry or dried in place.

The silane treatment coating may be cured at a temperature of betweenabout 40° C. and 180° C. The curing time is dependant upon the curingtemperature although this time is not crucial. It is sufficient just todry the article in the shortest possible time. Lower temperatures wouldexcessively lengthen drying times. After curing, a second treatmentsolution may be applied or the first treatment solution may bereapplied, and cured if desired. Curing times may be between 0.5 minutesand 1 hour but preferably a curing period of between about 0.5 minutesand 3 minutes is used. Curing will eventually take place even at roomtemperatures over a sufficient period of time. The metal substrate maybe painted immediately but this is not essential.

The examples below demonstrate some of the superior and unexpectedresults obtained by employing the methods of the present invention.

The standard pretreatments, comparative pretreatments and testing usedin the assessment of the efficacy of the present invention are asfollows:

Testing:

The accelerated corrosion tests were BS 6496 Acetic Acid Salt Spray foraluminium and BS 6497 Acetic Acid Salt Spray for zinc, ASTM B117 NeutralSalt Spray for steel and zinc. Both these methods were applied for 1000hour tests.

A shorter test was introduced to speed up the selection process andfound to give close correlation of the results within sets of testsubstrates to the salt spray method. This shorter test comprisedimmersing scored panels in a 2 wt % sodium chloride solution at 55° C.,pH 7±0.25, for 5 days and examining the extent of paint disbandment.

Paint adhesion was evaluated using reverse impact according to BS 3900part E3 and a modified cupping method where the paint film is scoredthrough to the metal substrate in a grid pattern of orthogonal linesspaced 1.5 mm apart to generate 100 individual squares of paint followedby cupping in accordance with BS 3900 part E4 to a fixed depth. Aftercupping, adhesive tape is applied to establish the degree of paintdetachment induced by the metal distortion. The loss is expressed as thenumber of squares detached (=percent of grid pattern).

Aluminium panels with powder coat paint were also subjected to apressure cooker test according to BS 6496 para 17.

Concentrates:

Pretreatment chemicals are normally supplied as a concentrate that isdiluted with water to generate the working solution. Two concentratedsolutions have so far been prepared that have exhibited stable storagecharacteristics:

1) 4 vol. % BTSE+2 vol. % APS in ethanol+water.

2) 8 vol. % BTSE+4 vol. % APS in ethanol+water.

A mixture of 20 vol. % BTSE+10 vol. % APS was found to be unusablebecause the solution gelled after −4 days. Although the gel did disperseto form a uniform clear solution on stirring with water, the supply of aconcentrate as gel would be impractical for most end users. We expect tobe able to produce a concentrate some where in the range 8 to 20 vol. %BTSE+4 to 10 vol. % APS.

Cyclic Fatigue Testing:

A typical cyclic fatigue test would be 500,000 cycles at an appliedcyclic force of +/− 1200 N at a frequency of 8 Hz. All the variantspassed this test without failure.

EXAMPLE 1 Electropaint

6″×4″ test panels were spray cleaned in Pyroclean® 1055 (a silicatedmulti-metal cleaner) for 3.5 minutes at 55° C. The panels were thenprocessed as follows for the standards against which the silanepretreatments were gauged:

Steel: This was conditioned in 2 g/l Parcolene® X for 30 seconds atambient, immersed in Bonderite® 26SF (a trication zinc phosphate) for 3minutes at 50° C. to produce a fine crystalline zinc phosphate coatingof −2.1 g/m². Post-rinse in Parcolene® 86 (a chrome III solution) at 1.5g/l followed by rinsing and drying.

Zinc: (electrogalvanized (EZ) and hot-dip galvanized (HDG))—The sameprocess conditions were used as above.

The silane mixture shown in Table 1 are as follows:

(1) 2 vol % BTSE+1 vol % γ-APS.

TABLE 1 Corrosion (mm paint loss × % of score line) Steel ElectrogalvBonderite ® Silane mix Bonderite ® Silane mix Electropaint 26SF (1) 26SF(1) 1000 hr salt 0 1-3 × 100 — — spray 120 hr hot 0 0 2 × 75 1-4 × 100salt soak

EXAMPLE 2 Powder-coat Paint

Steel: A cleaner-coater was used that simultaneously cleaned andphosphated the metal surface. The panels were sprayed with Pyrene® 2-68at 60° C. for 3 minutes to produce an iron phosphate coating weight of1.1 g/m². This coating was given a post-rinse of Pyrene Eco Seal® 800 at5 g/l.

Zinc (EZ & HDG): A cleaner-coater was used as above but one formulatedfor zinc and aluminium. The panels were sprayed with Pyrene® 2-69 at 60°C. for 3 minutes to produce a coating weight on steel of 0.65 g/m². Thephosphate coating was post-rinsed with Pyrene Eco Seal® 800 at 5 g/l.

Aluminium: The same processing as for zinc above.

Table 2 shows the results of 1000 hour salt spray testing on powdercoated steel, hot-dip galv and aluminium.

The silane mixture shown in Table 2 are as follows: (1) 2 vol % BTSE+1vol % γ-APS.

TABLE 2 1000 hour salt spray testing on powder coated steel, hot-dipgalv and aluminium 1000 hr Salt Spray Results Corrosion (mm paint loss ×% o score line) Steel Hot dip galv. Aluminium Powdercoat Pyrene ® SilanePyrene ® 2- Silane Pyrene ® Silane Type 2-68 mix (1) 68 mix (1) 2-69 mix(1) Polyester/ 5-6 × 1.2 × Tot. paint 2 × 10 — — Epoxy 100 100 lossPolyester — — 1-8 × 100 2-6 × 20 0 0

Table 3 shows the results of adhesion testing of powder coat films. Thesilane mixture shown in Table 3 are as follows: (1) 2 vol % BTSE+1 vol %γ-APS.

TABLE 3 Adhesion testing of powder coat films Hot dip galv. AluminiumPolyester Pyrene ® Silane Pyrene ® Silane powder coat Steel 2-69 mix (1)2-69 mix (1) Paint Loss (%) N/A 100 0 36074 0

Table 4 shows the results of different BTSE/APS ratios in a 120 hr hotsalt soak on zinc.

TABLE 4 120 hr hot salt soak on zinc 120 hr hot salt soak on zinc silanecomposition (mm paint loss × % of score line) 2% BTSE + 2% APS 1-2 × 80 2% BTSE + 1% APS 1 × 100 2% BTSE + 0.5% APS 1-3 × 90  2% BTSE + 0.25%APS >10 × 100 2% BTSE + 0.3% APS 1 × 100 1% BTSE + 2% APS 1 × 90  0.5%BTSE + 2% APS 1 × 40 

EXAMPLE 3 Silane Pretreatment

The preparation of the silane solution (2% v/v BTSE+1% v/v γ-APS and (2%v/v BTSE+0.5% v/v γ-APS) was as follows:

3 parts by volume of BTSE was mixed with 4 parts by volume ofdemineralised water and 17 parts by volume of industrial methylatedspirits. This mix was left for 7 days. The γ-APS was hydrolyzed beforeuse by adding 5% v/v water, mixing and leaving for 24 hours. Thissolution was then diluted with demineralised water to give 0.5 and 1%v/v γ-APS and the pH adjusted to 6 with acetic acid. Enough hydrolyzedBTSE was then added to the neutralised γ-APS to give 2% BTSE.

For the application to steel as a pretreatment it has been found thatthe pH of the silane solution can adversely affect some grades and/orsurface finishes of steel by causing rusting. We have found thatapplications of solution at pH 6 have been consistently reliable for allthe variants we have encountered so far. For ease of operation this pHhas also been adopted for zinc and aluminium, although lower pH's couldbe tolerated when applying silanes to these substrates.

The substrates are immersed for 30 seconds in the solution, allowed todrain for a short period, then dried in an oven at 85° C.

The electropaint panels were coated with a layer of 30 μm thicknesswhile the powder coated components were given 60 to 90 μm paint films.Panels were then subjected to accelerated corrosion testing and paintfilm adhesion testing.

EXAMPLE 4 Coil-coat Applications on Three Substrates

γ-APS/BTSE was treated on ACT CRS, Baycoat Hot Dipped Galvanized Steel(HDG) and Galvalume® panels. The control panels were B1000 P60 DIW forCRS, Chromate treatment on Baycoat production line for HDG andGalvalume. Galvalume panels were painted with primer (m856-016) and topcoat (22-20752); HDG panels were painted with primer (PMY 0154) and topcoat (SPG 0068), made by Lilly Industries; CRS panels were painted with80G Newell White Polyester (408-1-w976), made by Specialty CoatingCompany. They are all polyester base paint.

Table 5 shows the corrosion test results (Salt Spray Test Results(mm)(Polyester Coil paint)) for the following compositions.

1. γ-APS 0.5% vol.+BTSE 2% vol. pH=5

2. γ-APS 1% vol.+BTSE 2% vol. pH=5

3. Control treatment

TABLE 5 Salt Spray Test Results (mm) Galvalume ® 744 HDG 1080 Treatmenthrs. hrs. CRS 336 hrs. Solution Edge Scribe Scribe Scribe 1 2.0 ± 0.3 04.4 ± 0.2 3.6 ± 0.4 2 1.6 ± 0.1 0 4.1 ± 0.3 0.9 ± 0.1 3 3.4 ± 0.6 0 7.0± 1.0 4.4 ± 0.4

EXAMPLE 5 Treatment for CRS

The treatment used to treat ACT cold-rolled steel panels was a solutioncomposed of 2-6% γ-APS, 0.5-2% BTSE, 0.01-0.1% acetic acid, 5-15%alcohol and 80-90% deionized water. River Valley paint (polyester base)was the top coat for the silane treated and zinc phosphate/chrometreated panels (purchased from ACT). The panels were tested in a saltspray chamber for 216 hours.

Table 6 shows the test results.

TABLE 6 Salt spray test results of River Valley painted CRS panels.Treatment Creepage, mm γ-APS/BTSE 0.7 ± 0.3 Zinc Phosphate/Chrome 1.0 ±0.2

EXAMPLE 6

Aluminium alloy grade 5251 test panels were processed using γ-APS/BTSEas follows:

1. The aluminium sheets were Immersion cleaned in Pyroclean 630 (25 g/l,70° C., 5 minutes). (Pyroclean® 630 is a silicated alkaline, non-etchcleaner).

2. The sheets were cold water rinsed.

3 parts by volume of BTSE was mixed with 4 parts by volume ofdemineralised water and 17 parts by volume of industrial methylatedspirits. This mix was left for 7 days.

3. The γ-APS was hydrolyzed before use by adding 5% v/v water, mixingand leaving for 24 hours. This solution was then diluted withdemineralised water to give 0.5 and 1% v/v γ-APS and the pH adjusted to6 with acetic acid. Enough hydrolyzed BTSE was then added to theneutralised γ-APS to give 2% BTSE. The cleaned and rinsed sheets wereimmersed in these BTSE/γ-APS solutions for 30 seconds.

4. The panels were then dried at 80° C.

As a comparison 5251 panels were processed in chromate pretreatment asfollows:

1. Immersion cleaned in Pyroclean 71 (25 g/l, 70° C., 5 minutes).(Pyroclean 71 is a non-silicated alkaline no-etch cleaner).

2. Cold water rinsed.

3. Immersed in Aluma Etch 701 (40 g/l Aluma Etch® 701 additive, 50° C.,2 minutes).

4. Cold water rinsed.

5. Immersed in 10% v/v nitric acid (to remove smut left by the etch).

6. Cold water rinsed.

7. Immersed in Bonderite 711™ (15 g/l, 40° C., 4 minutes, coating weight0.74 g/m²). (Bonderite 711 is a process designed to give yellow chromateconversion coatings suitable for overpainting).

8. Cold water rinsed.

9. Demineralised water rinsed.

10. Dried in a current of compressed air.

Both the chromated and silane treated panels were painted with:

(a) A 2 pack liquid paint (believed to be polyurethane) used in thearchitectural aluminium industry prepared by mixing 6 parts paint with 1part hardener and stoved at 120° C. for 3 minutes to produce a paintfilm thickness of 50 μm.

(b) A polyester powder-coat paint stoved at 200° C. metal temperaturefor 10 minutes to produce a minimum paint film thickness of 60 μm.

The panels were subjected to 1000 hours BS 6496 Acetic Acid Salt Spray,the panels painted with the 2 pack liquid paint were subjected to 4 mmreverse impact and 3 mm and 7 mm Erichsen Indentation/1.5 mm cross hatchadhesion tests. The results for the tests are shown in tables 7 and 8respectively.

TABLE 7 1000 hours Acetic Acid Salt Spray Test 2 pack liquid paintPowder coat Paint Removal Paint Removal mm × % mm × % mm × % mm × %Bonderite ® 711 2.5 × 5 2.5 × 20 0 0 (chromate) BTSE 2%/γ-APS 1% 0 0 0 0BTSE 2%/γ-APS 0.5% 0   2 × 10 0 0

TABLE 8 Reverse Impact and 3 mm and 7 mm Erichsen Indentation/1.5 mmCross Hatch Adhesion Tests 2 pack liquid paint Erichsen/Cross Hatch 3 mmIndent 7 mm Indent Reverse Impact % Adhesion % Adhesion Bonderite ®Partial removal to 100 100 711 10 mm (chromate) BTSE 2%/γ-APS Partialremoval to 100 95 1% 10 mm BTSE 2%/γ-APS Partial removal to 100 100 0.5%10 mm

EXAMPLE 7 Pretreatment for Coil Aluminium

Aluminium (alloy grades 3005 and 3105 test panel were processed asfollows:

1. Immersion in Pyroclean 630 (25 g/l, 70° C., 5 minutes).

2. Cold water rinsed.

3. Immersed in the silane solution for 10 seconds, passed through rubbersqueegee rollers to remove excess liquid and oven dried at 80° C. Silanesolutions used:

BTSE 2%+γ-APS 1%, pH 4.9

BTSE 2%+γ-APS 0.5%, pH 5.0

As a control 3005 and 3105 test panels were cleaned and rinsed as aboveand coated with a chromium coating rinse process as follows. Accomet C®(a chrome containing no-rinse process supplied by Albright and Wilson)was diluted to 12.5% v/v, poured over the panels which were then spun toremove the excess liquid and dried at 105° C. The chromium coatingweight on the panels was 45 mg Cr/m².

The panels were painted with Polycoat polyester paint supplied by Bolligand Kemper. The panels were cured at a peak metal temperature of 243° C.for 40 seconds. The dry paint film thickness was 17 μm.

The panels wer subjected to 1000 hours BS 6496 Acetic Acid Salt Sprayand a T bend adhesion test (to ECCA-T20 [1992] specification). Theresults are shown in tables 10 and 9 and 10.

TABLE 9 1000 hours Acetic Acid Salt Spray Paint Removal 3005 Alloy 3105Alloy mm × % mm × % Accomet C (Cr no rinse) 1 × 10 1 × <5 BTSE 2%/γ-APS1% 1 × 5 0 BTSE 2%/γ-APS 0.5% 1 × 10 1 × 5

TABLE 10 T Bend 3005 Alloy 3105 Alloy OT ½T OT ½T Accomet C (Cr noCracking No Cracking No rinse) only. Removal. only. Removal. BTSE2%/γ-APS 1% Cracking No Cracking No only. Removal. only. Removal. BTSE2%/γ-APS Cracking No Cracking No 0.5% only. Removal. only. Removal.

EXAMPLE 8 Rubber Bonding

Current practice in metal to rubber bonding, as used extensively in theautomotive industry for shock absorber and anti-vibration mountings, isto phosphate the metal parts, then apply a primer coating followed by atopcoat to which the rubber is bonded. From processed parts supplied tovarious manufacturers the applicants have established that a silaneapplication to the metal surface followed by the topcoat (no primercoating) produces a metal-rubber bond of strength and durability equalto the current system.

Metal parts have been processed in two different silane mixtures (2%BTSE+0.5% APS pH 5.5, 2% BTSE+1% APS pH 5.5) both at ambient for 30seconds followed by drying at 100° C. and subjected to cyclic fatiguetesting to determine the strength and failure mode of the compositestructure.

Ultimate strength measurements:

2% BTSE+0.5% APS 7834 N

2% BTSE+1.0% APS 8635 N

In all cases the failure occurred within the rubber and not at ametal-rubber interface. For the current practice a value >3500 N isrequired.

EXAMPLE 9 Long-Term Corrosion Resistance Assesment

CRS, HDG 70G and aluminium 3003 were selected as test substrate.Alkaline cleaner Brent Chem clean 1111 (AC1111) which is similar toParker 338, was selected as cleaner for CRS and HDG. The substrates wererinsed in AC 1111 (at 15 g/l) for 2 minutes at 140° F. Because a strong,uninhibited alkaline cleaner, such as AC1111, will attack and dissolvealuminium, AC 1220 was selected to clean aluminium 3003. The AC 1220 wasused at 5% by volume at 130° F. The substrates were treated withAPS/BTSE solution as prepared in Example 3, then cured at 220° F. for 30minutes. Infrared spectroscopy was considered to be one of the mostpowerful tools for the study of molecular structure and composition foryears. It is well documented that siloxane group has a unique absorptionat about 1000 cm⁻¹ in IR spectrum. Therefore, Nicolet AVATAR-360 FTIRwas used to characterized the films deposited on metal surface byAPS/BTSE before and after alkaline clean. After IR spectra werecollected, these substrates were washed in the cleaner specified above.The IR spectra were collected again. The spectra before and after theclean for the same treatment and the same substrate were compared. Ifthe absorption of siloxane group disappears after the clean, itindicates the siloxane film is removed.

Evaluation Results:

IR spectra indicated that alkaline cleaner can not remove those siloxanefilms on CRS and HDG and silicate cleaner can not remove the siloxanefilms on aluminium, neither. The results are shown in Table 11.

TABLE 11 Appearance of Siloxane Absorption in IR Spectrum Aluminium HDGCRS Before After Before After Before After γ-APS/BTSE Yes Yes Yes YesYes Yes

What is claimed is:
 1. A composition comprising γ-aminopropyltriethoxysilane, at least one multi-silyl-functional silane having the general structure

and an alcohol or mixture of alcohols, wherein Z is C₁-C₆ alkylene; each R³ is ethyl; n is 2; the ratio of γ-aminopropyltriethoxysilane to said at least one multi-silyl-functional silane is in the range 4:1-1:8 by volume; and the content of said alcohol or mixture of alcohols is up to 15% by eight.
 2. The composition according to claim 1, wherein the multi-silyl-functional silane is 1,2-bis-(triethoxysilyl)ethane.
 3. The composition according to claim 1, wherein the composition additionally comprises an acid.
 4. The composition according to claim 3, wherein the acid is selected from the group consisting of acetic, oxalic, formic and propionic acid.
 5. The composition according to claim 1, wherein the composition additionally comprises water.
 6. The composition according to claim 1, wherein the concentration of said at least one multi-silyl-functional silane in the composition is between about 0.1% and about 10% by volume.
 7. The composition according to claim 1, wherein the concentration of γ-aminopropyltriethoxysilane in the composition is between about 0.1% and about 10% by volume.
 8. The composition according to claim 1, wherein the ratio of γ-aminopropyltriethoxysilane to said at least one multi-silyl-functional silane is in the range 2:1-1:4 by volume.
 9. The composition according to claim 1, wherein the ratio of γ-aminopropyltriethoxysilane to said at least one multi-silyl-functional silane is in a ratio of greater than 1:2 by volume.
 10. The composition of according to claim 1 wherein the alcohol is ethanol or methanol.
 11. A composition comprising at least one amino silane, a multi-silyl-functional silane, an acid and an alcohol or mixture of alcohols, wherein the multi-silyl-functional silane is 1,2-bis-(triethoxysilyl)ethane; the ratio of said at least one amino silane to 1,2-bis-(triethoxysilyl)ethane is in the range 4:1-1:8 by volume; and the content of said alcohol or mixture of alcohols is up to 15% by weight.
 12. The composition according to claim 11, wherein said at least one amino silane has the structure

wherein R is selected from the group consisting of hydrogen, C₁-C₂₄ alkyl, and C₂-C₂₄ acyl, and each R may be the same or different; X is selected from the group consisting of a bond, C₁-C₆ alkylene, C₁-C₆ alkenylene, arylene and alkylarylene; and, each R¹ is individually selected from the group consisting of hydrogen, C₁-C₆ alkyl, C₁-C₆ alkenyl, arylene and alkylarylene.
 13. The composition according to claim 12, wherein each R is individually selected from the group consisting of hydrogen, ethyl, methyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl, ter-butyl and acetyl.
 14. The composition according to claim 12, wherein wherein each R¹ is individually selected from the group consisting of hydrogen, ethyl, methyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl, ter-butyl and acetyl.
 15. The composition of claim 11, wherein the at least one amino silane is γ-aminopropyltriethoxysilane.
 16. The composition according to claim 11, wherein the acid is selected from the group consisting of acetic, oxalic, formic and propionic acid.
 17. The composition according to claim 11, wherein the composition additionally comprises water.
 18. The composition according to claim 11, wherein the concentration of said multi-silyl-functional silane in the solution is between about 0.1% and about 10% by volume.
 19. The composition according to claim 11, wherein the concentration of said at least one amino silane in the composition is between about 0.1% and about 10% by volume.
 20. The composition according to claim 11, wherein the ratio of said at least one amino silane to said multi-silyl-functional silane is in the range 2:1-1:4 by volume.
 21. The composition according to claim 11, wherein the ratio of said at least one amino silane to said multi-silyl-functional silane is in a ratio of greater than 1:2 by volume.
 22. The composition according to claim 12, wherein each R is ethyl.
 23. The composition of according to claim 11 wherein the alcohol is ethanol or methanol. 